(CNN)ISIS has claimed responsibility for a horrific day of carnage that devastated southern Syria on Wednesday.

At least 166 people were killed in a suicide bombing and attacks that took place in the southern province of Suwayda, the United Nations Office for the Coordination of Humanitarian Affairs in Syria tweeted.

ISIS said it was responsible, in a statement posted on the ISIS-affiliated Telegram channel. ISIS said "soldiers of the caliphate" first attacked security positions and government targets in Suwayda city. After the attackers ran out of ammunition, they detonated their explosive vests, ISIS said.

Syrian forces thwarted two other attacks in As-Suwayda, shooting and killing two attackers before they blew themselves up, state-run media added.

In recent weeks, Syrian forces have intensified an offensive in southern Syria to eliminate ISIS pockets that remain in the area. A well-known rescue group called the White Helmets say they have been caught in the crossfire.

The White Helmets have operated in opposition-held parts of Syria throughout Syria's seven-year civil war. But in recent weeks, President Bashar al-Assad's forces have swept through rebel territory, recapturing scores of southern villages in a Russian-backed offensive.

ISIS affiliate Khaled ibn al-Walid Army remains in southern Syria's Yarmouk river basin. Russian and Syrian regime forces have been pummeling the area with airstrikes in an attempt to rout out the group.

Hundreds of thousands of people are believed to have been displaced by the military campaign.